Virgin Birth Discovered in Pit Vipers

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Deadly pit vipers are capable of virgin birth, scientists now
find, joining their constrictor relatives in the ability to
reproduce without sex.

Female pit vipers can also conserve sperm after sex for at least
a whopping five years, shedding light on the lengths these
serpents will go to in order to procreate, researchers added.

Asexual reproductionis
common among invertebrates — that is, animals without
backbones — and is rare in vertebrates, but not unheard of. For
instance,
the komodo dragon, the world's largest living lizard, has
given birthvia parthenogenesis, in which an unfertilized egg
develops to maturity. Such
virgin births have also been seen in sharks
at least twicenow, and occasionally in birds and amphibians.

Scientists had even discovered a boa constrictor that could
reproduce by virgin birth. Now, for the first time,
researchers find that pit vipers can do so as well.

Virgin births

Evolutionary and population geneticist Warren Booth at North
Carolina State University at Raleigh and his colleague Gordon
Schuett investigated a female copperhead (Agkistrodon
contortrix) kept at the North Carolina Aquarium at Fort
Fisher. Over the past five years, she had come into contact with
only one male snake — a corn snake (Pantherophis
guttatus) — and interbreeding between the two species is
considered unlikely or impossible.

In 2009, this copperhead gave birth to a litter of four offspring
that were outwardly normal in appearance, two of which were alive
at birth. Analysis of DNA from the mother, one live offspring and
one of the stillborn progeny revealed no signs of genes from a
father, suggesting
a true virgin birth.

"Instead of wasting eggs, which are costly to produce and a
finite resource, parthenogenesis may represent an alternate means
of reproduction to overcome this," Booth said. In light of the
loss of habitat these snakes face, virgin births might allow this
species to hold on a little longer, he added.

Sperm banking

The scientists also looked at a female eastern diamond-backed
rattlesnake (Crotalus adamanteus) that was captured
while sexually immature and kept isolated from males in captivity
for at least five years. In 2010, it gave birth to a total of 19
healthy offspring. Genetic analysis of the mother and each of the
offspring revealed genes from a father in each of the progeny.
This suggested the single mother had mated with one or more males
before her capture and conserved the sperm for at least five
years until she was mature enough to reproduce.

Females of a number of species are known to
store sperm for a variety of purposes — for instance, to keep
sperm around until their egg cells are ready. However, this may
be the longest recorded case of sperm storage in any vertebrate,
and the first confirmed instance in snakes.

"Mating opportunities may be rare in many species," Booth said.
It therefore makes sense "for a species to have solved this
problem through the evolution of mechanisms by which mating can
occur when the opportunity arises and the spermatozoa stored
until needed."

Altogether, these findings show that this lineage of snakes "is
particularly well-adapted to insuring the production of offspring
when conditions may be adverse," Booth noted.

There may even be practical applications from this work.

"Researchers interested in understanding the mechanisms behind
successful long-term sperm storage may want to take a closer look
at this group, particularly in light of its potential application
to both human and livestock sperm storage," Booth said.

Booth and Schuett detailed their findings online Oct. 10 in the
Biological Journal of the Linnean Society.